As is well known, a bipolar junction transistor (BJT) comprises a collector, a base, and an emitter. A schematic representation of a cross sectional view of a prior art bipolar junction transistor 100 is illustrated in FIG. 1. A collector 110 made of silicon is isolated by shallow trench isolation (STI) structures 120. The STI structures 120 can be formed from silicon oxide or tetraethyloxysilane (TEOS) or other similar material. A silane deposition process is then employed to deposit silicon over the collector 110 and over the STI structures 120 to form a base layer 130.
As is well known in the art, the silicon that is deposited over the collector 110 forms an epitaxial base portion 140. The silicon that is deposited over the STI structures 120 forms a polysilicon base portion 150. Lastly, an emitter 160 of polysilicon is formed on top of the epitaxial base portion 140.
Recently a method has been developed that replaces the polysilicon emitter on the epitaxial base portion of a bipolar junction transistor with an epitaxially grown mono-silicon emitter. The use of an epitaxially grown mono-silicon emitter significantly reduces the emitter access resistivity. The method is described in a paper by P. Deixler et al. entitled “QUBiC4X: an fT/fmax=130/140 GHz SiGe:C-BiCMOS Manufacturing Technology with Elite Passives for Emerging Microwave Applications” published in IEEE BCTM 12.3, pp. 233-236, 2004. This paper will hereafter be referred to as the “Deixler” reference. The Deixler reference describes the operational parameters and characteristics of an epitaxially grown mono-silicon emitter in a bipolar junction transistor.
In the method described in the Deixler reference, a two stage deposition process is used to epitaxially grow the mono-silicon emitter. The epitaxial base portion of the bipolar junction transistor is formed in a first deposition stage. Then the epitaxially grown mono-silicon emitter is formed in a second deposition stage.
Therefore, there is a need in the art for an improved system and method that can form an epitaxially grown mono-silicon emitter in a bipolar junction transistor. Specifically, there is a need in the art for an improved system and method that can form both an epitaxially grown mono-silicon emitter and a base portion of a bipolar junction transistor in a single deposition process.
Before undertaking the Detailed Description of the Invention below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like.
Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior uses, as well as to future uses, of such defined words and phrases.